It has been known to provide a grapple attachment which mounts to the bucket of a front loader-type tractor, such as that previously disclosed in U.S. Pat. No. 4,285,628. Such grapple systems typically include an upper, movable jaw member which is hinged so as to generally pivot or rotate about a horizontal axis between an open and closed configuration relative to the fixed bucket assembly. By swinging from an open to a closed configuration, the movable jaw member is able to trap and pin the target load within the mouth of the bucket. Once securely pinned within the bucket, the load may be lifted and transported to the desired destination.
In previous grapple designs, the actuating mechanism for controlling the position and relative orientation of the movable jaw member with respect to a stationary jaw assembly typically incorporates a direct linkage between a point on the fixed jaw assembly and a corresponding point on the pivoting jaw member. Generally, the direct linkage assembly includes a linear actuating power unit such as a hydraulic cylinder, which is physically located between the fixed jaw assembly and the pivot axis of the movable jaw member. The hydraulic cylinder, being so positioned, is capable of extending and contracting the effective length of the connecting linkage, thereby causing the movable jaw member to generally rotate about the horizontal pivot axis between an opened and closed configuration. As a consequence of this type of connecting linkage and actuation configuration, there are certain orientations of the jaw member which render the actuating mechanism with a very short effective lever arm, and hence very little mechanical advantage. While in such orientations, the resultant force ultimately transferred to the movable jaw member is quite small, because of the short lever arm, and as a consequence large, powerful actuators and associated heavy structural support members are often required to accommodate a broad or full range of grapple jaw movement.
Therefore, with particular regard to grapple assemblies which are adapted to be mounted and secured to a front-end loader or equipment adapted to carry a grapple, there is and continues to be a need for a grappling assembly that incorporates an actuating mechanism which is capable of maintaining a significant mechanical advantage over a broad range of grapple jaw movement, thereby reducing actuating power requirements and actuator related structural requirements.